1. Field of the Invention
The present invention relates to a locking device for locking a rod of a fluid pressure cylinder at any stopping position as desired.
1. Description of the Prior Art
When a rod of a fluid pressure cylinder is moved by the weight of the load in case fluid pressure is decreased or lost due to power suspension, accident or other causes during operation, it is not only dangerous for the operator but deleterious to other equipment and devices because these may be damaged. To prevent such an accident, a locking device for locking the rod is provided in such system.
As the locking device for the fluid pressure cylinder, a device using an eccentric cam has been proposed in Japanese Patent Publication Laid-Open 3-66905.
This locking device comprises a set of brake members arranged around an axial line perpendicular to the rod with the rod placed therebetween so that the brake members can be eccentrically rotated, and these brake members are always pushed by a spring in such a direction that a thick portion of each of these members is engaged into a gap between the member and the rod (a direction to lock the rod), while, in a normal case, the two brake members are controlled by a brake cylinder so that they are not in locking state. If fluid pressure supplied to the brake cylinder is decreased due to an accident, the control is released, and if resilient force by the spring is applied on the two brake members and the rod is moved in a specific direction, the thick portions of the two brake members are engaged into a gap between the brake members and the rod so that the movement of the rod is locked.
Although the locking device as proposed above is advantageous in that the rod can be locked when fluid pressure is decreased or lost due to accident, the brake cylinder is arranged with its axial line in parallel to the rod and the brake piston is moved in an axial direction of the rod. As a result, the locking device is very long in axial direction and the device must be designed in large size.
Also, because the locking is achieved in a specific direction, if the rod is to be locked in two reciprocating directions, it is necessary to arrange two sets of the locking devices in series in axial direction of the rod. This means that larger space is required for installation.
Further, the locking force may be different according to each brake member because of the possible manufacturing errors of the brake piston or the brake members, and it is very difficult to adjust or control the locking force.